Evidence for a single multifunctional polypeptide chain on gramicidin S synthetase 2 obtained from a wild strain and mutant strains of Bacillus brevis.

The structures of the gramicidin S synthetase 2 s (GS 2, heavy enzyme) from a wild strain and mutant strains of Bacillus brevis have been studied by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). The GS 2s used were obtained from a wild strain and group IV of mutant strains (BII-3, BI-3, BI-9) which lacked one specific amino acid activating activity. SDS polyacrylamide gel electrophoresis of GS 2 bound to a radioactive substrate showed that: first, in the case of the wild enzyme, the radioactivity of the substrate amino acid was detected only in the polypeptide with a molecular weight of about 280,000, regardless of the amino acid species used as substrate; secondly, in the case of the mutant enzyme, the radioactivity of the amino acid which could be activated by the enzyme was also associated with the protein band with a molecular weight of about 280,000. Regardless of the enzyme species tested, a pantothenic acid residue was also present in the protein band with a molecular weight of about 280,000. These results suggest that GS 2 is a multifunctional one polypeptide enzyme and the mutant-type GS 2s from BII-3 (proline-lacking), BI-3 (valine-lacking), and BI-9 (leucine-lacking) are also multifunctional enzymes having molecular weights identical to that of the wild-type enzyme.